The present disclosure relates to certain systems and methods for evaluating permeability and/or microproppant placement in subterranean formations.
In order to efficiently produce hydrocarbons from a subterranean formation, the formation should be sufficiently conductive in order to allow the hydrocarbons to flow to the wellbore. Various treatments for increasing the conductivity of a subterranean formation have been developed, including hydraulic fracturing treatments.
Fracturing tight formations of unconventional reservoirs, such as formations containing shale, tight sandstone formations and coal bed formations, requires special considerations. For example, shale, coal and other types of formations can have a permeability of approximately 1 millidarcy (mD) or less. Hydraulically fracturing such formations typically forms a complex fracture network that includes primary fractures (and branches thereof) and microfractures (including natural microfractures and induced secondary microfractures) in a zone of the formation surrounding the wellbore. For example, the microfractures can extend from a tip and edges of a primary fracture or a branch thereof and extend outwardly in a branching tree-like manner from the primary fracture. The microfractures can extend transversely to the trajectory of the primary fractures allowing them to reach and link natural fracture both in and adjacent to the trajectory of the primary fractures. The microfractures can exist and be formed in both near-wellbore and far-field regions of the zone, as well as regions located adjacent to primary fracture branches. As a result, the microfractures can give more depth and breadth to the fracture network.
In the absence of proppant particulates, the microfractures tend to close back once the hydraulic pressure placed on the formation is released or decreased. Conventional or traditional proppant particulates are often too large to prop the microfractures open. As a result, due to their size, conventional proppant particulates cannot be easily placed in microfractures. Allowing the microfractures to close cuts off a significant portion of the fracture network and ultimately prevents the production of valuable hydrocarbons therefrom.
In order to address this issue, micro-proppant particulates having a size sufficient to allow the particulates to be placed in microfractures have been developed. The microproppant particulates are included in the pad fluid stages of the fracturing treatment. Including microproppant particulates in the pad fluid places the microproppant particulates in the fissure openings to and otherwise in the microfractures as soon as they are opened or created. By holding the microfractures open, the microproppant particulates help maintain fluid communication between the microfractures and the primary fractures. Conventional proppant particulates are then included in the proppant-slurry stages of the fracturing treatment and placed in the primary fractures and branches to help ensure that fluid conductive flow paths to the wellbore are maintained. However, the stimulation of tight formations often involves complex interactions between the formation and the injected fluid-proppant mixture, which may depend on various factors relating to the mechanical properties and/or composition of the formation itself as well as those of the micro-proppants. For example, the deposition of an incomplete monolayer of microproppants in a microfracture may inhibit the conductivity of that microfracture.